Neutrino physics
Ryan Patterson Caltech
HCPSS August 21, 2020 (Figure from “Report of the 2013 Community Summer Study”)
HCPSS 2020 Neutrino oscillations Three neutrino flavors 휈 휈휇 휈휏 depends on… e
mixing matrix UPMNS 2 mass-squared splittings mij
Observed using… solar, atmospheric, reactor, and accelerator 휈 sources
Sun imaged with 휈 Cosmic rays Daya Bay NPP Fermilab (Super-K)
Ryan Patterson 3 HCPSS 2020 Neutrino oscillations Three neutrino flavors 휈 휈휇 휈휏 depends on… e
mixing matrix UPMNS 2 mass-squared splittings mij
8 Atmospheric 휈휇 flux vs. zenith angle Solar neutrino fluxes ( B decay)
Super-K collab., 1144 live-days (2000) SNO collab., Phys. Rev. C 72, 055502 (2005)
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Ryan Patterson 4 HCPSS 2020 - The presence of neutrino oscillation implies neutrino mass → see functional dependence later
- Oscillations do not provide a measure of the neutrino masses → depends only on differences in squared masses
So what are the actual masses?
Ryan Patterson 5 HCPSS 2020 • Cosmological observations sum of neutrino masses. Best limits: mi < 0.12 eV (95% C.L.) CMB TT/TE/EE + LSS + BAO
• 훽-decay kinematic measurement effective 휈e mass, a.k.a. m훽:
• 0휈훽훽 decay process (if Majorana-휈-mediated) effective mass m훽훽:
kinematic measurement n p - 0휈훽훽 e
휈 ×
e- n p
Ryan Patterson 6 HCPSS 2020 Kinematic mass measurement: KATRIN
Precision spectroscopy near the endpoint of tritium beta decay
Mertens /KATRIN(Nu2020)
Ryan Patterson 7 HCPSS 2020 Kinematic mass measurement: KATRIN
Precision spectroscopy near the endpoint of tritium beta decay
Mertens
/KATRIN(Nu
2020 )
Ryan Patterson 8 HCPSS 2020 Kinematic mass measurement: KATRIN
Precision spectroscopy near the endpoint of tritium beta decay
Mertens
/KATRIN(Nu
2020 )
KATRIN latest: m훽 < 1.1 eV (90% C.L.)
Ryan Patterson 9 HCPSS 2020 Kinematic mass measurement: alternatives
• Spectroscopy through cyclotron radiation: “Project 8”
Oblath
/Project /Project
8 8
(Nu
2020 )
• 163Ho electron capture: study resulting excitation spectra instead using microcalorimetric techniques.
Ryan Patterson 10 HCPSS 2020 S. R. Elliott and P. Vogel, Ann. Rev.
Nucl. Part. Sci. 52, 115 (2002) 2020 HCPSS signature 훽 훽 휈 0 Example still present as a background. present still 11 훽 훽 휈 2 : double beta decay beta double disallowed. enrichment fraction) enrichment at endpoint, at ⨯
searches practical in isotopes where single beta decay is betadecaysinglewherein isotopes practicalsearches
훽 multiple good candidate isotopes available and in use and in isotopesavailable candidategood multiple
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- mass (total or some compensating or some if not feature resolution - and passive shieldingand passive - General approach General kinematically 0
• •
Ryan Patterson Ryan Neutrinoless 0휈훽훽: many techniques
Cryogenic semiconductor detectors (GERDA [Ge], MAJORANA [Ge], Scintillating bolometers LEGEND [Ge]) Large volume scintillator detectors (CANDLES [Ca], CUORE [Te], (KamLAND-Zen [Xe], SNO+ [Te]) CUPID [Mo])
Liquid and HP gas TPCs Tracking detectors (EXO [Xe], NEXT [Xe], LZ [Xe]) (NEMO, SuperNEMO [Se, others]) 12 J. Detweiler (Nu2020)
13 J. Detweiler (Nu2020) .) .) % C.L % % C.L.) % C.L % 90 ( 90 90 ( ( yr yr yr 26 26 25 10 10 10 ⨯ 14 ⨯ ⨯ 1.07 1.8 3.2 > > > Zen) Zen) - turning lifetime turning uncertainty limits requires limits 3 KamLAND 훽 - ( (GERDA) (CUORE) 훽 2 limits at present: at limits m
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factor of factor 훽
- ordering regime. ordering backgrounds at bay at backgrounds mass inverted coverto Over next decade, increase decade, next Over keeping while mass are poorly known poorly are limits into into limits that elements matrix nuclear Complication: Complication: Best Best
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휈
• • •
Ryan Patterson Ryan 0 Neutrino mass: why so small? H t Z W
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cosmo cosmo heaviest lightest neutrino neutrino Ryan Patterson 15 Neutrino mass: why so small? H t Z See-saw mechanism? – Heavy (possibly GUT-scale) RH neutrinos W alongside light LH neutrinos: b 휏 c
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cosmo cosmo heaviest lightest neutrino neutrino Ryan Patterson 16 Neutrino mass: why so small? H t Z See-saw mechanism? – Heavy (possibly GUT-scale) RH neutrinos W alongside light LH neutrinos: b 휏 c
s 휇
d u
e
) GeV Would imply that the physics of neutrino mass is
connected to extremely high energy scales. ( mass
Potential new physics signatures in oscillation expts: non-unitarity, non-standard interactions, >3 neutrinos, large
extra dimensions, effective CPTv, decoherence, neutrino decay, …
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Now textbook material, the see-saw mechanism goes back to P. Minkowski (1977); oscillations cosmo
M. Gell-Mann, P. Ramond and R. Slansky (1979); and T. Yanagida (1979) cosmo heaviest lightest neutrino neutrino Ryan Patterson 17
Flavor structure ← flavor symmetry ? → → |Ue3| ≠ 0 |U휇3| = |U휏3| ? (recent discovery) (“maximal mixing”) u c t d s b
e 휇 휏 2
approx. 1:1:1 ratio symmetry gauge
휈e 휈휇 휈휏
← ← (mass)
What flavor symmetry can produce this pattern of mixings and masses, and how is that symmetry broken? More broadly: what are the dynamical origins of fermion masses, mixings, and CP violation? Ryan Patterson 18 HCPSS 2020 Flavor structure
|Ue3| ≠ 0 |U휇3| = |U휏3| ? (recent discovery) (“maximal mixing”) Experimental question: 2 sin 휃23 ≠ 0.5 ? Non-maximal mixing?
If so, which way does it break? 2
approx. 1:1:1 ratio (mass)
Standard parametrization of PMNS matrix:
Ryan Patterson 19 HCPSS 2020 CP violation New source of CP violation required to explain baryon asymmetry of universe part-per-billion level of matter/antimatter asymmetry in early universe
Neutrino CPv allowed in 휈SM, but not yet observed …due so far to the experimental challenge, not physics!
Leptogenesis1 is a workable solution for the baryon asymmetry, but need to first find any leptonic (neutrino) CPv
sin 훿 ≠ 0 ? Leptonic CP violation?
1 M. Fukugita and T. Yanagida (1986); rich history since then.
Ryan Patterson 20 HCPSS 2020 휈 Ryan Patterson a simple a simple question: Far Notice: - - - - An inverted hierarchy implies hierarchy inverted An <1.5% mass degeneracy <1.5% mass hierarchy Theoretical Cosmology Experimental approach to and 0 → → 휈 flavor flavor and mass generation interpretation of - 훽 reaching implications for such heavier or lighter electron Are the Would at…?? hint 훽 and and Majorana Majorana nature of and and frameworks astrophysics m 훽 - rich states (cf.: for than . 휋 + 휈 휈 / 휋 3 0 ? ) 휈 1 21 & 휈 2 P.PRD al., et Guzowski (mass)2 92 , 012002 HCPSS HCPSS 2020 ( 2015 )
Flavor: A core problem for 21st century particle physics
Nucl. Phys. B B Phys. Nucl. Fiorentin Re Marzola, Bari, Di Flurry of theoretical work. 2 Discrete flavor groups (A4, S4, Δ(3n ), …) often combined with GUTs. Non-trivial flavor texture
in heavy sector. 893
Emphasis on genuine predictive power. Explicit , (2015) 122 connections between low energy observables and leptogenesis. Often immutable preferences for mass hierarchy
and 휇/휏 asymmetry
JHEP Varzielas, Medeiros de King de Björkeroth, Anda,
Nucl. Phys. B B Phys. Nucl. Molinaro Meroni, Hagedorn,
06
, 141 (2015) , 141
891 , 499 , (2015) 499
Ryan Patterson 22 HCPSS 2020
Flavor: A core problem for 21st century particle physics
Nucl. Phys. B B Phys. Nucl. Fiorentin Re Marzola, Bari, Di Flurry of theoretical work. Pascoli and Zhou, JHEP 06, 73 (2016) Discrete flavor groups (A4, S4, Δ(3n2), …) often Flavor symmetry A4 ⨯ Z2 ⨯ Z4; flavon-induced combined with GUTs. Nonconnections-trivial flavor between texture flavor mixing and CLFV,
in heavy sector. and… 893
Emphasis on genuine predictive power. Explicit , (2015) 122 connections between low energy observables and leptogenesis. Often immutable preferences for mass hierarchy
and 휇/휏 asymmetry
JHEP Varzielas, Medeiros de King de Björkeroth, Anda,
Nucl. Phys. B B Phys. Nucl. Molinaro Meroni, Hagedorn,
06
, 141 (2015) , 141
891 , 499 , (2015) 499
Ryan Patterson 23 HCPSS 2020 - A lot of the neutrino sector is practically probed through the study of neutrino oscillations
- Oscillation experiments come in many shapes to access particular pieces of the intertwined puzzle
Ryan Patterson 24 HCPSS 2020 Reactors at short baselines
• 휃13 was last mixing angle to be bracketed. Previously a bit of 휈e just known to be rather small relative to 휃12, 휃23 + • Reactor expts. use inverse beta decay: 휈͞ e + p e + n prompt e+ signal, delayed n-capture signal
(Double Chooz)
Outer buffer region surrounded by PMTs Gamma catcher (undoped scintillator)
Target region (Gd-doped scintillator)
Ryan Patterson 25 HCPSS 2020 2020 Double Chooz RENO HCPSS 26 Buffer catcher Gamma
Target
Cartoon Daya Bay Patterson Ryan Ryan Reactors at short baselines
• Clean measurement of a single parameter, 휃13: - Baseline too short for neutrino mass hierarchy to matter (via matter effects) - 휈͞ e → 휈͞ e process is CP symmetric 2 - L/E too small for m 21 to matter much
Daya Bay result: Daya Daya Bay experiment holds best measurement BayCollab., Phys. Rev.Lett.
old but useful Daya Bay plot
121
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27 Reactors at medium baselines • Same E (reactor source), increase L by ~30⨯ 2 - Now tuned to m 21-driven oscillations (“solar” oscillations) - 휃13 small / subdominant now (휃12 the leading mixing angle) - The faster oscillations are blurred out by energy resolution as well
KamLAND measured terrestrially what Y. Meng the other experiments saw with solar
neutrinos (where MSW effect is central!) (Nu
2020 )
JUNO: Future experiment high precision and perhaps to observe dominant and subdominant oscillations together ( mass hierarchy) 28 Reactors at medium baselines • Same E (reactor source), increase L by ~30⨯ 2 - Now tuned to m 21-driven oscillations (“solar” oscillations) - 휃13 small / subdominant now (휃12 the leading mixing angle) - The faster oscillations are blurred out by energy resolution as well
KamLAND measured terrestrially what Y. Meng the other experiments saw with solar
neutrinos (where MSW effect is central!) (Nu2020)
M. Smy (NNN 2018)
JUNO: Future experiment high precision and perhaps to observe dominant and subdominant oscillations together ( mass hierarchy) 29 Long-baseline oscillation experiments • Higher E (~GeV), longer L, more accessible channels - 휈휇 → 휈e / 휈휇 / 휈휏 : enough E to make charged lepton partners in CC interactions (though 휈휏 somewhat specialized (e.g., OPERA expt.)) - Multiple relevant PMNS parameters - Larger mass splitting relevant - Large (massive) far detector needed
Example accelerator source (NuMI beamline diagram):
Ryan Patterson 30 HCPSS 2020 휈휇 hundreds of kilometers 휈휇 휈휏
Near Detector 휈e Far Detector
휈휇 survival (or “disappearance”):
experimental data are consistent with unity (i.e., maximal mixing) …to leading order
Ryan Patterson 31 HCPSS 2020 휈휇 hundreds of kilometers 휈휇 휈휏
Near Detector 휈e Far Detector
휈e appearance:
…plus potentially large CPv and
matter effect* modifications! 2
* 휈e see different potential than 휈휇,휏 when (mass) propagating through matter (here, the earth) ⇒ a hierarchy-dependent effect !
Ryan Patterson 32 HCPSS 2020 (From PDG) (for antineutrinos, x → -x and 훿 → -훿)
Ryan Patterson 33 HCPSS 2020 For fixed L/E = 0.4 km/MeV
P(휈⎺휇→휈⎺e) vs. P(휈휇→휈e) for a 2 GeV neutrino in NOvA → Dependence on 훿 and 휈 mass hierarchy
Ryan Patterson 34 HCPSS 2020 For fixed L/E = 0.4 km/MeV
P(휈⎺휇→휈⎺e) vs. P(휈휇→휈e) for a 2 GeV neutrino in NOvA → Dependence on 훿 and 휈 mass hierarchy
small 휈¯e rate
large 휈e rate
Ryan Patterson 35 HCPSS 2020 For fixed L/E = 0.4 km/MeV
P(휈⎺휇→휈⎺e) vs. P(휈휇→휈e) for a 2 GeV neutrino in NOvA → Dependence on 훿 and 휈 mass hierarchy 2 → P ∝ sin 휃23 [approx.]
Ryan Patterson 36 HCPSS 2020 T2K, NOvA, and DUNE baselines for a single L/E value.
These differ solely in the influence of matter effects
Illustrative only! Other parameters are held fixed, and experiments (esp. DUNE) probe a range of neutrino energies.
Ryan Patterson 37 HCPSS 2020 NOvA Far Detector and event display
T2K Far Detector (Super-K) and event display
Ryan Patterson 38 HCPSS 2020 Example LBL data set (Latest NOvA)
39 Latest T2K and NOvA results Intertwined, multidimensional parameter space. Looking at just a slice here.
Let’s walk through some observations and conclusions - If you’re looking at this without the audio, sorry!
High-level observations: - Some CP violation is preferred over no CP violation - Hierarchy preference is still slight, but the favored choice (NH) leads to tension elsewhere - Non-maximal mixing / upper octant preferred
40 Future LBL Experiments • Major leap in sensitivity for neutrino sector questions - Also: supernova neutrinos (see later) - Also: many beyond-the-SM physics searches, incl. baryon number violation
DUNE HyperK (T2HK) - very long baseline (1300 km) - Same baseline as T2K (295 km) - LAr TPC detector (70 kton) - Water Cherenkov detector - Superb PID, low thresholds - Massive (260 kton) - New beam from Fermilab - Upgraded beam from J-PARC
Ryan Patterson 41 HCPSS 2020 Future LBL Experiments DUNE CPv sensitivity Key neutrino sensitivity points (10 yrs, “staged” exposure)
- CPv @ 5휎 for >50% of 훿 values [Both] - CPv @ 3휎 for ~75% of 훿 values [Both] - 훿 resolution 7° – 17°/23° [DUNE/HK] - Mass hierarchy in 1 – 2 yrs: >5휎 [DUNE] - Mass hierarchy at 10 yrs;: 5 – 7휎 (atm. 휈) [HK] 8 – “20휎+” (beam 휈) [DUNE]
- Octant determination >5휎 if 휃23 is outside of roughly [43°, 49°] [Both]
Remarkably similar in mainline 휈 sector performance, save for hierarchy Complementary in accessible supernova and solar channels, BSM channels, detection techniques, systematics
Ryan Patterson 42 HCPSS 2020 S. Woosley and T.Janka Supernova neutrinos Nature Physics . 99% of energy released in a core-collapse supernova is
carried away by neutrinos (cf.: 0.01% carried away by light) 1
. Rich information embedded in neutrino signal: , 147 (2005) • Supernova physics: core-collapse mechanism, black hole formation, shock stall/revival, nucleosynthesis, cooling, … • Particle physics: flavor transformations in core, collective effects, mass ordering, nuclear equation of state, exotica
Key interaction channels Garching Garching model ( (few to 40 MeV) Neutronization Accretion Cooling 휈 + e elastic good directionality
휈͞ e CC inv. 훽 decay; Gd doping 27
in water detectors will M ⊙
help see the neutrons )
휈e CC accessible in argon! unique flux features 휈 NC flavor agnostic, but hard to work with 43 HCPSS 2020 S. Woosley and T.Janka Supernova neutrinos Nature Physics . 99% of energy released in a core-collapse supernova is
carried away by neutrinos (cf.: 0.01% carried away by light) 1
. Rich information embedded in neutrino signal: , 147 147
• Supernova physics: core-collapse mechanism, black hole ( formation, shock stall/revival, nucleosynthesis, cooling, … 2005
• Particle physics: flavor transformations in core, collective ) effects, mass ordering, nuclear equation of state, exotica
Single galactic supernova event Astropart. Astropart. Phys. → would yield thousands of C. Lunardini, interactions in the large Solar 휈 detectors DSNB predictions
Diffuse supernova neutrino backg’d 79
, , 49 49
Should be there. ( 2016 Atmospheric 휈 Not yet observed. Best limits from ) Super-K within factor of two of model prediction(s).
Ryan Patterson 44 HCPSS 2020 Brief look at light sterile neutrinos
(different from sterile neutrinos as DM, massive RH sterile partners as in mass generator or leptogenesis, etc.)
Ryan Patterson 45 HCPSS 2020 Sterile neutrinos • Here: Light sterile neutrinos that mix with familiar active ones - distinct from, e.g., sterile neutrinos as DM, massive RH sterile partners invoved in mass generation or leptogenesis, generic heavy neutral leptons, etc. • Only three light active neutrinos (from Z width)
• In the 1990s, LSND expt reported anomalous 휈e and 휈¯e appearance - could not be accommodated with only three neutrinos - one interpretation is oscillations involving a 4th (sterile) neutrino MiniBooNE • MiniBooNE followed up at higher E (same L/E) - reported 5휎 excess • Many null results using various techniques over past two decades - KARMEN, Bugey, Super-K, MINOS(+), ICARUS, IceCube, Planck, NOvA, T2K, Daya Bay, DANSS, PROSPECT, …
Ryan Patterson 46 Sterile neutrinos • But neither a nail in the coffin nor an unambiguous signal has been forthcoming - Model dependence in comparing across different techniques (e.g., disappeance vs. appearance searches; 3+1 vs. 3+n models) - No clear L/E oscillation signature - Background worries (well-founded or not) (e.g., MiniBooNE can’t distinguish 훾 from e)
• Upcoming and most directly analogous measurement will be from MicroBooNE and the broader Fermilab “short baseline” program
- same appearance channel(s) as LSND and MiniBooNE: 휈휇→휈e (and anti-휈) - and, LAr TPC detectors can rule out 훾 backgrounds - but, exposure isn’t enormous, and control of systematics not yet demonstrated
• A number of LBL, SBL, reactor, spallation neutron source, and cosmological measurements are underway or in development (Editorial comment: none will soon solve the issue in the first bullet) Ryan Patterson 47 HCPSS 2020 So much didn’t fit in the limited time! • Atmospheric neutrinos - Wide range of energies, copious source, range of physics topics - LBL beam experiments generally outperform for standard PMNS measurements • Ultra high energy neutrinos (extraterrestrial sources) - Very large detectors or detector arrays (e.g., IceCube, ARA) - Addressing astrophysical questions mostly, but also some particle physics (e.g., cross sections at very high energies) • Geoneutrinos - Neutrinos generated from within the earth radiologically - Addressing questions of planetary structure and formation • Solar neutrinos - The pioneering neutrino oscillation laboratory - Now, addressing solar physics (e.g., solar metallicity) more than particle physics • 휈 interactions - interactions on nuclear targets poorly constrained - recent: 1st measurement of 휈 coherenet scattering (eventual DM background?) • Precision PMNS - toward neutrino “unitarity triangle” - flavor structure → model constraints • Neutrino-related BSM physics - Non-standard interactions, large extra dimensions, CPTv, neutrino tridents, ...
Ryan Patterson 48 HCPSS 2020